In a bicycle transmission a gear is normally used to transfer the torque applied by the rider on pedal cranks to the rear wheel through a power transmission means. The power transmission means fits on the gear and can be a chain or a toothed belt.
DE 20 2004 006 544 U1 describes an oval, preferably elliptically shaped gear, intended to reduce rider fatigue by increasing the level of efficiency. The shape of the gear should be suited to the thrusting movements generated through the muscle power of the legs. It has proven to be a disadvantage, however, that the known gear only marginally improves the level of efficiency and also has a non-round pedaling feel, because the foot experiences different accelerations during one rotation of the pedal crank.
DE 10 2013 000 689 A1 and WO 2015/030576 also disclose non-round gears with multiple segments in the circumferential direction and a constant curvature radius within each segment, resulting in the outer contour having the same curvature. Only at the transfer point between adjacent segments, the constant curvature radius of a first segment changes to another curvature radius of a second segment, so that the curvature of the outer contour changes only at these transfer points. As soon as one of these transfer points engages in the pulling segment of a chain running on the gear, the rider feels a clear change in the pedal speed, which is perceived as unpleasant and annoying.
The effect of the non-round pedaling feel is also known from other transmissions for which efficiency level improvements were attempted. DE 10 2010 033 211 B4 describes a transmission of this type, in which a planet gear runs on a fixed sun gear and a crank arm rotates together with the planet gear, wherein the crank arm is mounted rotatably on a pedal crank. The sun gear, planet gear, and crank arm are all contained in the same crankcase, and the pedal crank is supported in a common crankcase by a guide roller in a guideway that is also contained in the crankcase. The guide roller spins freely and with lateral play on in the guideway, so the non-round pedaling feel in the circumferential direction of the gear is even stronger due to the free-spinning guide roller.
There is a need for a gear that improves the pedaling feel of a bicycle transmission.